Communication in fluid medium using motor modulation

Abstract

Aquatic vehicles may use electric motors for propulsion, such as brushless motors. As an example, a speed of these motors can be controlled using a pulse-width-modulated (PWM) electrical signal that varies the motor speed by varying pulse parameters within the PWM signal. PMW modulation can cause the motor to emit significant acoustic noise into the environment. In a fluid medium, such as aquatic environment, such noise can be detected with hydrophones or other acoustic sensors. The subject matter described herein can include modulating a signal provided to a motor to provide a communication signal to be mechanically (e.g., acoustically) emitted by the motor in a fluid medium, such as an underwater medium. In this manner, the motor can function both as a source of propulsion, and as an electroacoustic transducer (e.g., a transmitter).

The claimed invention is: 
     
         1 . An electromechanical communication system, comprising:
 an electrically-powered propulsion motor mechanically coupled to a vehicle, the propulsion motor configured to provide mechanical propulsion in a fluid medium;   a control circuit coupled to the propulsion motor, the control circuit configured to generate an electrical signal to the propulsion motor including a portion corresponding to operating energy for the propulsion motor to use in providing thrust, and a portion corresponding to a transmission signal to be acoustically transmitted through the fluid medium by the propulsion motor acting as an electromechanical transducer.   
     
     
         2 . The electromechanical communication system of  claim 1 , comprising an acoustic receiver configured to receive the transmission signal and to provide an electrical signal representative of the received transmission signal. 
     
     
         3 . The electromechanical communication system of  claim 2 , wherein the fluid medium is water; and
 wherein the acoustic receiver comprises an acousto-electric transducer.   
     
     
         4 . The electromechanical communication system of  claim 2 , comprising a signal processor configured to process a signal received from the acoustic receiver to determine at least one of a location, a distance, a relative bearing, or a locus of relative bearings, relative to the vehicle housing the electrically-powered propulsion motor. 
     
     
         5 . The electromechanical communication system of  claim 4 , wherein the signal processor is configured to determine a relative degree of angular error between an acoustic receiver location and a specified axis extending from the vehicle housing the electrically-powered propulsion motor. 
     
     
         6 . The electromechanical communication system of  claim 5 , wherein the portion corresponding to the transmission signal includes a first modulation signal to be acoustically transmitted in a first direction and a different second modulation signal to be acoustically transmitted in a different second direction; and
 wherein the signal processor is configured to determine the relative degree of angular error comprises determining a relative indication of a received magnitude of the first modulation signal as compared to a received magnitude of the second modulation signal.   
     
     
         7 . The electromechanical communication system of claim I, wherein the portion corresponding to the transmission signal includes information encoded using a frequency modulation scheme. 
     
     
         8 . The electromechanical communication system of  claim 1 , wherein the portion corresponding to the transmission signal includes information encoded using an edge polarity encoding scheme. 
     
     
         9 . The electromechanical communication system of  claim 1 , wherein the portion corresponding to the transmission signal includes information encoded using an amplitude modulation scheme. 
     
     
         10 . A method for controlling an electrically-powered propulsion motor, the propulsion motor configured to provide mechanical propulsion in a fluid medium, the method comprising:
 generating an electrical signal to the propulsion motor including:
 a portion corresponding to operating energy for the propulsion motor to use in providing thrust; and 
 a portion corresponding to a transmission signal to he acoustically transmitted by the propulsion motor acting as an electromechanical transducer. 
   
     
     
         11 . The method of  claim 10 , wherein the portion corresponding to the transmission signal includes a first modulation signal to be acoustically transmitted in a first direction and a different second modulation signal to be acoustically transmitted in a different second direction. 
     
     
         12 . The method of  claim 10 , wherein the portion corresponding to the transmission signal includes information encoded using at least one of a frequency modulation scheme, a frequency-shift keying (FSK) scheme, an edge-polarity encoding scheme, or an amplitude modulation scheme. 
     
     
         13 . The method of  claim 10 , wherein the transmission signal is added to the portion corresponding to the operating energy for the propulsion motor. 
     
     
         14 . The method of  claim 10 , wherein the transmission signal is established by modifying the portion corresponding to the operating energy. 
     
     
         15 . A method for receiving an acoustic signal transmitted by an electrically-powered propulsion motor, the propulsion motor configured to provide mechanical propulsion in a fluid medium, the method comprising:
 using an acoustic receiver, receiving a transmission signal acoustically transmitted by the propulsion motor acting as an electromechanical transducer;   processing the received signal to provide an electrical signal representative of the received transmission signal; and   using the electrical signal, determining an indication of a location of the acoustic receiver relative to the propulsion motor;   wherein the transmission signal is at least one of added to a signal corresponding to the operating energy for the propulsion motor or established by modifying the signal corresponding to the operating energy for the propulsion motor.   
     
     
         16 . The method of  claim 15 , wherein the fluid medium is water; and
 wherein the acoustic receiver comprises an acousto-electric transducer.   
     
     
         17 . The method of  claim 15 , wherein determining the indication of the location of the receiver includes determining at least one of a location, a distance, a relative bearing, or a locus of relative bearings, relative to a vehicle housing the electrically-powered propulsion motor. 
     
     
         18 . The method of  claim 17 , wherein determining the indication of the location of the receiver includes determining a relative degree of angular error with respect to a specified axis extending from the vehicle housing the electrically-powered propulsion motor. 
     
     
         19 . The method of  claim 18 , wherein the transmission signal includes a first modulation signal acoustically transmitted in a first direction and a second different modulation signal acoustically transmitted in a second different direction; and
 wherein determining the relative degree of angular error comprises determining a relative indication of a received magnitude of the first modulation signal as compared to a received magnitude of the second modulation signal.   
     
     
         20 . The method of  claim 15 , comprising generating steering guidance using the indication of the location of the receiver relative to the propulsion motor.